Boeing's 787 Dreamliner No. 2, on the ground at Boeing Field for more than three weeks, returned to Everett on Thursday after "small amounts of debris" were found inside its fuel tanks.
Flight tests can't resume until the tanks are cleaned out.
Boeing spokesman Scott Lefeber said the cleaning is expected to be completed "pretty quickly," though he would not be more specific.
He described the debris as "particulates" left in the tank. "We've refined the manufacturing inspections to make sure it doesn't happen again," he said.
Thursday's return to Everett was the second Dreamliner's only flight since the jet first flew Dec. 22.
